Products that are presently available to whiten teeth include a variety of different ingredients, but the primary active ingredient is a peroxide source such as hydrogen peroxide. In high concentrations, hydrogen peroxide can be irritating to the teeth and/or gums. In addition, hydrogen peroxide is an unstable molecule that is prone to decomposition, especially in aqueous environments. This presents difficulties in terms of formulating a stable composition for consumer consumption. Thus, alternative oxidizing agents with improved stability are desired.
Peroxysulfuric acid, and its salts, the peroxysulfates, are powerful oxidizing and stain removing agents. They are currently used for a variety of industrial and consumer purposes, including swimming pool treatment and denture cleaning. The most common peroxymonosulfate oxidizing agent is potassium peroxymonosulfate, commonly referred to as MPS.
Potassium monoperoxysulfate has seen limited use in dental whitening compositions because of its instability in aqueous solution, especially in aqueous solution near or above neutral pH While potassium monoperoxysulfate is somewhat stable in aqueous solutions at acidic pH, it is more stable either as a solid or in an anhydrous formulation, and it is most active as an oxidizing agent (and tooth whitening agent) in an aqueous solution at pH 5-8. Anhydrous formulations typically include primarily hydrophobic polymers in a hydrophobic base. While these can achieve good stability, they often show poor dispensing characteristics. Thus, there has been difficulty formulating monoperoxysulfate based compositions with good rheological properties (dispensing characteristics) and good stability and whitening efficacy.
Improved tooth whitening formulations are desired which combine the relative stability of monoperoxysulfate salts in an anhydrous environment, with effective whitening and dispensing characteristics.